Field of the Invention
The present invention relates to a method of laser welding of an automotive light and relative automotive light obtained using said method.
Description of the Related Art
The term automotive light is understood to mean indifferently a rear automotive light or a front automotive light, the latter also known as a headlight.
As is known, an automotive light is a lighting and/or signalling device of a vehicle comprising at least one external automotive light having a lighting and/or signalling function towards the outside of the vehicle such as for example a sidelight, an indicator light, a brake light, a rear fog light, a reverse light, a dipped beam headlight, a main beam headlight and the like.
The automotive light, in its simplest form comprises a container body, a lenticular body and at least one light source.
The lenticular body is placed so as to close a mouth of the container body so as to form a housing chamber. The light source is arranged inside the housing chamber, which may be directed so as to emit light towards the lenticular body, when powered with electricity.
The method of manufacture of an automotive light, once assembled the various components, must provide for the attachment and hermetic sealing of the lenticular body to the container body.
Such sealing and attachment is usually performed by welding so as to create a weld bead between the perimetral profiles, respectively, of the lenticular body and the container body placed in contact with each other.
Naturally, the welding may also regard other components of a more complex automotive light, for example arranged inside the housing chamber.
A process of laser welding of polymeric bodies particularly of an automotive light makes it to combine a transmissive polymeric body, capable of transmitting a laser radiation, and an absorbent polymeric body, capable of absorbing the laser radiation. In the present case, the laser radiation is transformed into heat when it encounters the absorbent polymeric body which heating locally transfers heat to the transmissive polymeric body, as far as a softening and a local melting of both polymeric bodies, which thus join firmly to each other.
The absorbent polymeric body of an automotive light may be constituted, for example, by the container body, while the transmissive polymeric body of a automotive light may be constituted, for example, by the lenticular body, which closing the container body forms a housing chamber housing a light source of the automotive headlight.
Said housing chamber is delimited at the perimeter by the perimetral profiles of the container body and of the lenticular body which, placed in contact with each other, are sealed by the formation of a weld bead, at which the interpenetration of the materials of the lenticular body and the container body takes place.
Of course, the absorbent and transmissive polymeric bodies may be composed generically of further polymeric components of the automotive headlight.
As regards the laser equipment to be used, this generally comprises:                at least a laser source, which can for example be a semiconductor laser source,        a system of optical fibres grouped together in a “bundle” which serves to transport the laser light produced by the laser source, in the vicinity of the lenticular body,        an optical fibre support which has the purpose of holding the optical fibres in position in the vicinity of the lenticular body. For example, the support may be a metal body with housing holes in which the optical fibres are contained. They may be attached by a system in which the head of a screw, which is screwed to the metal support of the optical fibres, presses a polymer washer which expands radially. The optical fibre is thus blocked by the polymer washer on the housing hole walls,        an optical system, with the function of a collimator, which has the purpose of modifying the divergence of the laser beam coming out of the fibre and directing said beam towards the weld bead.        
Typically, as a collimator, a negative light guide is used, i.e. a light guide formed of reflective walls inclined with respect to the optical axis of the fibre.
In the simplest version of the prior art (FIG. 1), the light guide has a geometry with reflecting walls inclined with respect to its optical axis and the optical fibre is positioned in the vicinity of the upper opening of the light guide and along the optical axis. Again in the simplest case, the system proves to be symmetric on the transversal plane of the light guide, i.e. the inclination of the reflective walls of the light guide is the same with respect to the optical axis. Longitudinally, the light guide extends along the trajectory which defines the weld bead.
A parameter which is related to the distribution of the optical fibres along the trajectory of the weld bead is the distance or pitch ‘d’ between the fibres, the minimum value of which is given by the dimensions of the optical fibres and of the attachment system and the maximum value of which is conditioned by the minimum value of energy deposited on the bead.
This configuration is generally used when the system, i.e. the light to be welded, has a simple geometry.
Where the radiation energy deposited on the weld bead needs to be increased, for example when the thickness of the lenticular body is high with a consequent increase of the absorption by the material, two rows of optical fibres may be used on the same light guide (FIGS. 2-3). The optical fibres may be arranged on the same transversal plane (FIG. 2) or on different transversal planes (FIG. 3).
In the first case the optical fibres belonging to the same transversal plane are pointed on the same region of the weld bead.
In the second case the optical fibres, lying on different planes, point in different areas of the weld bead with the aim of making the irradiation more even.
The lenticular body may however have a complex geometry for stylistic and aerodynamic reasons. On account of such, the weld bead proves not conformal to the lenticular body, i.e. it may not be a translation of the lenticular body. However a continuous and homogeneous irradiation along the weld bead must be ensured even if the lenticular body has an uneven surface.
With the solutions of the prior art, i.e. with the configuration in which the fibres are inclined with respect to the optical axis on a plane transversal to the weld bead, a non-uniform irradiation is created due to the presence of shadow zones. In FIG. 4, the presence of a shadow zone in the irradiation of the weld bead in areas with complex geometries or irregular areas of the lenticular body has been highlighted. The same FIG. 4 also shows how, thanks to the present invention, it is possible to fill said shadow zone in order to obtain a uniform and regular weld, as better described below.
It follows that, in the case of welding automotive lights where the lenticular body usually has complex geometries (such as variations of concavities/complexity, grooves, ribs, protuberances, and the like), the solutions of the prior art of laser welding are not satisfactory in terms of quality of the weld bead generated.
In the light of all the above considerations, laser welding techniques are little used to date on automotive lights, especially if they have a complex geometry; such laser welding techniques are thus replaced by alternative welding techniques, such as friction, ultrasonic, hot-plate welding and the like.